1. Field of the Invention
This invention relates to a color cathode-ray tube panel having a front surface which is easier to view and more balanced in comparison with the conventional shadow-mask cathode-ray tube.
2. Description of the Prior Art
A color television cathode-ray tube includes a funnel-shaped main body having a rectangular open side, and a cylindrical neck portion, which accommodates three electron guns for the colors R, G, B, connected to the bottom of the main body. Affixed to the open side of the main body is a front panel comprising a transparent glass plate. The inner and outer surfaces of the front panel are formed to be curved. A shadow mask is disposed on the rear side of the front panel.
The original form of the panel of the conventional shadow-mask color television cathode-ray tube utilizes any portion extracted from a sphere, as shown in FIG. 6(A). There are a wide variety of these models presently employed in small-size tubes. Though such models are employed to some extent in large-size tubes as well, the majority have a panel surface that is asopherical owing to problems related to the doming phenomenon, temperature drift and convergence in the deflection yoke, or because of the need for a rectangular, flat screen. In general, as illustrated in (A) and (B) of FIG. 2, the radius R.sub.YO of the panel surface in the vertical direction is smaller than the radius R.sub.XO in the horizontal direction, and there are portions of the surface which extend in directions from which a picture is difficult to view or in directions which cause an increase in distortion of the picture.
Another problem is that increasing the doming phenomenon and enlarging the radius R.sub.YO to obtain a panel surface that is easy to view are contractory to each other in terms of their effects.
According to the shadow-mask configuration, the basic shape of a panel of the Trinitron (registered trademark) type using a color selecting mechanism of different shapes (in which the color selecting mechanism employs an aperture grill) utilizes part of a cylindrical shape shown in FIG. 6(B). The radius R.sub.YO of FIG. 2(B) defines a shape approximating a straight line. With regard to viewing ease, it is obvious that this configuration is superior to that of the present shadow-mask panel in view of the fact that there is little reflected external light from above. Whether a panel of this form can be used or must be used is decided by the basic structure of the aperture grill.
In a case where the cylindrical configuration is adopted as the panel for the shadow mask, it is required that the radius R.sub.YO of the shadow mask have a form approximating a straight line, and it is difficult to maintain this shape with a high degree of accuracy. In addition, this is a direction involving inconvenience with regard to doming. The cylindrical panel is suited to the Trinitron (registered trademark) system but has a shape that is inappropriate for a shadow-mask system.
The conventional shadow-mask panel surface shape is spherical, in which the radius R.sub.YO is equal to the radius R.sub.XO. In large-size tubes, however, most models have a smaller R.sub.YO.
If the panel surface is flatter, this is advantageous in terms of the ease with which the screen can be viewed. However, the panel surface has the shape presently in use because of physical limitations and other factors.
When a screen is viewed from the front, the degree of ease with which a picture can be seen is such that there is greater tolerance in the horizontal direction than in the vertical direction, assuming that the panel surface is spherical.
This problem can readily be understood by estimating the degree of ease with which an image or character on the panel can be read assuming a case in which the radius constituting the panel surface is reduced.
When the cylindrical panel of the Trinitron (registered trademark) system and the present shadow-mask panel are compared, it is a fact that the cylindrical panel, in which the radius R.sub.YO constituting the surface approximates a straight line, is easier to view, all other problems aside. It is obvious that a shadow-mask panel having a smaller radius R.sub.YO has a disadvantageous shape.
The Trinitron (registered trademark) system using the cylindrical panel is advantageous, but a problem is encountered with regard to providing a feeling of satisfaction to the impression of a well-balanced flat panel.
Structurally, the Trinitron (registered trademark) system is such that the panel has a shape obtained by cutting out a portion of a cylinder. Therefore, when it is desired that the degree of ease of convergence by the deflection yoke be made the same as that of a shadow mask, the radius R.sub.XO of the panel takes on a value smaller than of the radius R.sub.XO of the shadow-mask panel, and the difference between the radius R.sub.YO and the radius R.sub.XO is great. As a result, it is difficult to obtain the impression of a well-balanced flatness from the panel surface.
In a case where a panel for a Trinitron (registered trademark) having the same ease of convergence as that of the novel panel of this embodiment (described below) is given an outer-surface radius R.sub.YO of 30,000 R (in which the units are millimeters) and an inner-surface radius Ryi of 15,000 R, the result of calculations taking the edge of the glass into account as well is that the radius R.sub.XO becomes 1,456 R. The ratio of radius R.sub.YO to radius R.sub.XO is 20.6 to 1. This numerical value gives an impression much different from that of the shape described by the actual dimensions, but even in this design the difference between radius R.sub.YO and radius R.sub.XO is great and it is difficult to receive an impression of well-balanced flatness.
For comparison purposes in order to investigate this problem, a model was fabricated. The results of calculation are tabulated as shown below. The calculation of the ease of convergence was directed to the inner-surface radius. Since the most difficult direction among the X, Y and D directions is the D direction, the degree of ease of convergence of this cathode-ray tube can be inferred from the numerical value of the result of calculation in the D direction.
With regard to the degree of ease of convergence, an incidence angle, described below, is used (see FIG. 5). Assume that the deflection angle is 106.degree., and that the effective screen has dimensions of 544 mm in the X direction, 408 mm in the Y direction and 680 mm in the D direction.